1. Field of the Invention
The present invention relates to a self-drilling screw. In particular, it relates to a self-drilling screw with the function of reducing the manufacturing cost, increasing the screwing speed and allowing the user to engrave a mark on it.
2. Description of the Related Art
Generally, the length of the drilling portion of a self-drilling screw is designed according to the thickness of the object that the self-drilling screw is going to penetrate. An example of long drilling portion of self-drilling screw is described below.
Referring to FIG. 1, a conventional self-drilling screw 1 disclosed in U.S. Pat. No. 7,090,452 B2 comprises a head 11, a shank 12 extending from the head 11 and having a plurality of threads 121, a cutting member 13 extending from the shank 12, and an annular groove 14 provided between the shank 12 and the cutting member 13. Moreover, the cutting member 13 has a plurality of lengthwise cutting grooves 131 and a plurality of lengthwise wings 132 projecting therefrom. The annular groove 14 provides a volume to contain the debris from the cut object. While in operation, the conventional self-drilling screw 1 penetrates into an object with the cutting member 13 cutting said object. Meanwhile, the debris from said object temporarily accumulates in the annular groove 14.
However, the conventional self-drilling screw has several defects:    1. Due to the cutting member is long, the mold for making the cutting member of the self-drilling screw will be easily destroyed. The longer the cutting member is, the more serious damage the mold suffers. The life of the mold therefore shortens, and the manufacturing cost therefore increases.    2. Although the annular groove can help to contain the debris, it is not really benefit at obviating the debris. Since the debris is not easily obviated, it will be accumulated in the room between the screw and the object. Therefore, while in operation, the user suffers more resistance from the object. Therefore, while in operation, it wastes the user much labor to screw said self-drilling screw.
The present invention intends to provide an improved self-drilling screw which can efficiently drill into the object with less resistance and reduce the damage to the mold when shaping its cutting member.